All Questions

4
votes
2answers
119 views

Is it hypocritical to use AES-256 and RSA 2048 in the same application?

I see a common claim that AES-256 is the gold standard and is good future proofing, often in the same wind as "just use 2048-bit keys for RSA". Security documents seem to recommend both AES-256 and ...
0
votes
0answers
69 views

Yukel's Sieve - Factorization of Numbers into a Square Sieve

https://www.youtube.com/watch?v=liTTGeitpGQ https://www.youtube.com/watch?v=2nOwgiweyqc https://www.youtube.com/watch?v=rGwFsOG27DQ I came across these videos explaining a pattern that is found in ...
2
votes
1answer
37 views

Extracting Zip using Only the AES Key

I have set myself a little challenge, to see if I can decrypt my own text file from with a ZIP file... The AES Key from my encrypted ZIP is all I have managed to extract, how do I decrypt the ...
2
votes
1answer
65 views

Generating a key pair using a signature generated by an existing key

I’ve built an app in which each user has a private/public key pair and I want to generate a second one for them, however I cannot store the second private key anywhere. What would be the drawbacks ...
1
vote
0answers
40 views

Reason for including the public key of the key agreement in the KDF

I found the following text when looking up KDFs: In comparison, the so-called DHAES mode in IEEE 1363a mandates to use the binary representation of the sender’s public key as an input parameter. ...
-1
votes
1answer
39 views

Length extension attack for file download

I am trying to understand the length extension attack. I found this tutorial where the author performs length extension on a file download URL. Original URL: http://example.com/download?file=...
0
votes
1answer
60 views

Show that CPA-security implies security against plaintext recovery

Consider the following experiment: $k = Gen(1^n)$ $m \stackrel{u}{\in} \{0,1\}^{l(n)}$ $c = Enc_k(m)$ $m' = B(1^n,c)$ Define the winning event as $m' = m$. I would like to show that if the ...
6
votes
1answer
381 views

Does Shannon perfect secrecy imply a deterministic encryption algorithm?

Consider an encryption scheme $(Gen,Enc,Dec)$ where $Gen$ is the key generation algorithm, $Enc$ is the encryption algorithm, where $c \leftarrow Enc_{k}(m) $ is taken to mean that the message $m$ in ...
6
votes
3answers
183 views

Formal description of KDF1 and KDF2

I've seen many descriptions of KDF1 and KDF2 by now, but most documents simply point to specifications that are behind a pay wall. These standards are not specific to the KDF's; they just use these ...
0
votes
1answer
35 views

Burmester Desmedt Key agreement. Is the division a floating point one or an integer one

As I look upon Burmester Desmedt algorithm: I notice that the intermediate key $K_i$ is getting calculated as: $K_i=(k_{i+1}/k_{i-1})^{x_i} \mod p$ Thus I wonder wheher the division $k_{i+1}/k_{i-1}...
0
votes
0answers
5 views

How does Argon2id store salts in PHP? [migrated]

The PHP implementation of Argon2id generates a salt for the developer. How does the application keep track of this salt? As a developer, how do I account for backups and otherwise ensuring that I don'...
0
votes
0answers
6 views

Attempt to encrypt plain text with RSA public key throws error “unable to load Public Key” [migrated]

I received an RSA public key from a colleague by way of a pem file: ...
0
votes
2answers
54 views

Question about IV from CBC/AES-256

I'm developing a program to encrypt and decrypt a file with AES-256/CBC in Java. And I want it to be safe enough. In my case, I generated random AES key for each file to encrypt and decrypt them. My ...
1
vote
1answer
67 views

Is a hashing algorithm considered broken if a collision happens under $2^{n/2}$?

If for example we would find a hash collision for SHA256 with $h(x) = h(x')$ for $x \ne x'$ and $x, \space x' < 128$ bit (meaning both $x$ and $x'$ are smaller than 128 bit), would SHA256 be ...
1
vote
1answer
28 views

Restricting output of key derivation function

Are there any suitable key derivation functions that allow the output to have certain constraints applied to them?` I know you can choose a length in some functions (HKDF for example), but what about ...
12
votes
2answers
283 views

Does GCM (or GHASH) only provides 64-bit security against forgeries?

In a recent comment a doubt was voiced about my answer, which claims GCM to requires $2^{128}$ for a successful forgery. The doubt was that the square root needs to be taken meaning the security would ...
2
votes
1answer
49 views

Generating a small EDDSA curve

I have an application that would benefit from very small (e.g. 16-20 byte) EDDSA keys and small signatures. It's an application where the goal is more to deter DOS attacks than "hard" security, so ...
1
vote
0answers
53 views

Explaining Berlekamp-Massey Algorithm in simple/layman term?

My foundation in Mathematics is not great. But I would like to understand how Berlekamp-Massey Algorithm works and how it is used in lay-man terms. The only thing I find out there is the emphasis on ...
2
votes
0answers
44 views

Understanding LFSRs and Berlekamp-Massey Algorithm [duplicate]

I have a tutorial question which focuses on LFSRs and Berlekamp-Massey Algo (which is totally out of my syllabus). Please forgive me if my questions seem stupid. I'm given these information: {"...
1
vote
1answer
72 views

ChaCha with 64bit integers as a PRNG with streams

Can I use ChaCha with four rounds as a good non-cryptographic PRNG with different streams if I use 64 bit integers instead of the standard 32 bit integers? I need a bigger state and this seems the ...
-1
votes
1answer
52 views

Equivalence of cryptographic problems

Are integer factorization, discrete log and ECDH problems equivalent? I know that factorization and discrete log are equivalent but are one of those two problem equivalent with ECDH? Cand someone ...
3
votes
0answers
43 views

Is there a bilinear map on a non abelian group or non cyclic group?

I've recently been studying a pairing map on cryptography. In usual definition, a pairing map is always defined on the cyclic group G. Is it possible to construct a bilinear map on a non-abelian group ...
-2
votes
0answers
45 views

Classical definitions of encryption and masking

What would be the difference between encryption and masking, using the definitions around 30-50 years ago? Currently all articles link to RODO (GDPR requirements for data masking and anonymization) ...
0
votes
0answers
44 views

Can we build a zero knowledge mapping using public-key encryption?

I'm trying to understand if this design is possible. I want to build a mapping that is zero-knowledge, between a (pubkey, proposalId) => bytes form, without ...
4
votes
0answers
59 views

Key size, performance, and security tradeoffs for AES-GCM, CCM

AES can be used with 128, 192 or 256 bit keys and each one appears to have a performance vs security trade-off (What is the effect of the different AES key lengths?, What are the practical differences ...
0
votes
2answers
66 views

Why does Laravel only support AES-256-CBC?

Modern Laravel uses OpenSSL to provide AES-256-CBC encryption along with a MAC. However, I was under the impression that this is not a particularly secure approach. Why does Laravel only support AES-...
3
votes
1answer
49 views

SPHINCS and HORST: can we sign the same message twice?

I was reading about SPHINCS which uses layers of WOTS+ trees and a bottom layer of HORST trees. HORST is a few time signature scheme, using a selection function you can sign at least twice without ...
6
votes
4answers
3k views

One Time Pads and “Bit Flip” Attacks

One Time Pads and Vulnerability to "Bit-Flip" Attacks: I've seen it in this group, and apparently there are a (small) number of voices on the 'net opining that those relying on OTP are essentially "...
2
votes
2answers
109 views

Entropy of a random message chosen by an adversary from a subdomain

Assume we have a set of random bit strings: $S=\{s_1,...,s_n\}$, where each of them is of length $\lambda$ ($s_i\leftarrow\{0,1\}^{\lambda}$). We give the set $S$ to an adversary who picks one of the ...
3
votes
1answer
74 views

Golomb's Randomness postulates

In Handbook of applied cryptography, Golomb's randomness postulates are given: Let $s$ be a periodic sequence of period $N$. Golomb’s randomness postulates are the following. R1: In the cycle $s_N$ ...
0
votes
0answers
24 views

Dynamic accumulator with only non-membership witness

Goal: Construct a dynamic accumulator which can add elements and provide non-membership witnesses. I wanted to know if my construction is correct. Consider a group $Z_p$ where $p$ is prime number. ...
3
votes
1answer
60 views

In NIST modulus and key size recommendations is `group` equivalent to modulus and `key` equivalent to exponent?

Looking at the following NIST recommendations for a discrete logarithm, for 2016-2030 and beyond they list 3072-bit number for the group and 256-bit for the ...
2
votes
0answers
49 views

How can I determine the Hill cipher key in this case?

I have been struggling with a Hill cipher problem for many days, without any luck. I have the following ciphertext, which I know is an encrypted excerpt from an Edgar Allan Poe story: ...
4
votes
1answer
184 views

Can we estimate the loss of entropy when applying a N-bit hash function to and N-bit random input? [duplicate]

Someone pointed out recently to me that a cryptographic hash function " is not designed as a bijective mapping from N bit input to N bit output". So if I feed an N-bit cryptographic hash function ...
0
votes
0answers
27 views

Speeding up quotient determination in high-radix montgomery modular multiplication

In this paper Simplifying Quotient Determination in High-Radix Modular Multiplication, the authors have proposed to replace the original modulus $M$ in Montgomery Multiplication $ABR^{-1} \bmod{M}$ to ...
1
vote
1answer
40 views

64 bit clock cipher with CFB mode. One-byte defected from ciphertext. What is the number of bits defected from plaintext

I have a question from an exam; We encrypted a message of size 100 Bytes with CFB. In the transmission, byte number 12 got defected. How many bits defected will be in the decryption. The answer is 72 ...
1
vote
2answers
56 views

Integrity check of a binary firmware file with hash function

I need to provide a mechanism that it is possible to verify the integrity of a firmware image flashed on an embedded system. The procedure should be, that if someone has doubt on the firmware’s ...
0
votes
0answers
14 views

Setup phase in Ciphertext-Policy Attribute-Based Encryption

I am having hard time understanding the setup phase in Ciphertext-Policy Attribute-Based Encryption. What is the role of each parameter?
0
votes
0answers
19 views

What are dual codes and the codewords denoted by these dual codes in terms of trace?

I am currently reading a research paper (linked below) that mentions "Consider only maps that vanish at 0, their short codes $C_f$ and their duals $C_f^\perp$. The duals can be written as $C_f^\perp = ...
1
vote
1answer
57 views

Inverse of an element in a RSA group

Consider a RSA group $Z_N$ for $N=pq$, where $p,q$ are large prime numbers. Under strong RSA assumption, can an adversary efficiently compute the inverse of a random element $z$ from $Z_N$ without ...
1
vote
1answer
24 views

What is the link between the parity check matrix, double-error-correcting codes and APN permutations?

I am currently reading a research paper (linked below) which mentions that a map $f:V:=GF(2^{m}) \rightarrow V$ which vanishes at 0 is APN if it satisfies the condition that it is a binary code $C_{f}$...
1
vote
1answer
52 views

Alter plaintext through IV in block cipher AES in CBC mode

IV: 69bb375aa919c72aa561dd7b7ffacf66 Ciphertext: "c28ea025d10186510855d083747d6435c808d9857075abd9bfc54b094e60eaf3" Plaintext: "SEND ENCRYPTED DATA" I want to be able to change the resulting ...
3
votes
1answer
64 views

What's the difference between perfect security and unconditional security?

This paper refers to two distinct security models: perfect security and unconditional security. Until now, I knew of them as the same thing and equivalent to information-theoretic security. From the ...
0
votes
0answers
24 views

How long does it take for a secure enclave to sign something?

I have been looking into Intel SGX secure enclaves. The technology is cool, but the references about the technology (e.g. the programming manual and the tutorial) don't seem to have any information ...
1
vote
1answer
57 views

$m^b = z^b \pmod{n}$ - single solution $m = z$?

If i have the following equation: $$m^b = z^b \pmod{n}$$ Where all numbers are taken from the multiplicative group $\mathbb{Z}_n^*$. Suppose I know the values $z$ and $b$. Can I state that $z = m$, ...
1
vote
0answers
69 views

Finding generator element for multiplicative group of order $n$ - feasible?

Given a multiplicative group of order $n$, how hard is it to find a generator element (such that all other elements can be expressed as powers of that generator)? What would be the complexity?
1
vote
1answer
54 views

How secure is a 4 digit seed?

When I Use a 4 digit random number(e.g. 4468) as seed for a (manual) Stream cipher and straddle it to the length of the plaintext using a lagged fibonnacci generator, can this seed be found by brute ...
1
vote
1answer
64 views

One-time pad encryption - how does the receiving side decrypt the message?

If a message is sent using one-time pad scheme, which generates random bits in order to, for example, XOR them with the message's bits - how does the receiving side generate the exact series of bits ? ...
0
votes
1answer
38 views

Using the same RSA key for verifying a website and digital signature

We have the (same) RSA key for verifying a website and for digital signature. A user would send a nonce encrypted using the public key, the websites returns the nonce by decrypting it using the ...
1
vote
1answer
47 views

Proof of ignorance to prevent “double-spend”?

Suppose I have some knowledge that I want to transfer securely from Alice's computer to Bob's computer, and prove that future breaches to Alice's computer will not reveal that information to someone ...

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